The primary objective of this project is to gain an understanding of the role of middle-reiterated DNA sequences in gene expression. 1) A novel selection protocol will be used to establish a bank of clones containing developmentally regulated genes. The structure of repetitive DNA sequences in a number of clones will be compared and correlated with differential gene expression. We will also examine the stage-specific expression of a number of different cloned genes which contain a copy of a given repetitive DNA sequences. 2) The level of control for differential gene expression will be examined. The results of these experiments together with the analysis of clones containing developmentally regulated genes, will allow us to assign a probable role to repetitive DNA sequences. 3) The details of messenger RNA processing in Dictyostelium will be reexamined. Precursor-product relationships for individual mRNA species will be established. 4) The cloning and the structural analysis of transfer RNA genes will be continued. Particular attention will be paid to the occurrence of reiterated DNA sequences associated with the tRNA genes. In addition we will examine the synthesis and processing of transfer RNAs in Dictyostelium. 5) Studies of the gene organization of the ribosomal DNA repeat units in Dictyostelium will be completed.